Spin–orbit-coupled fermions in an optical lattice clock

Abstract

Spin–orbit coupling is implemented in an optical lattice clock using a narrow optical transition in fermionic 87Sr atoms, thus mitigating the heating problems of previous experiments with alkali atoms and offering new prospects for future investigations. Spin–orbit coupling is the root of many intriguing phenomena in condensed-matter physics, such as topological insulators. Researchers have been trying to simulate such condensed-matter systems with ultracold neutral atoms and other atomic techniques in order to understand the physics of these systems. However, realizing artificial spin–orbit coupling in ultracold quantum gases or other platforms is difficult, and most attempts have been plagued by heating effects. Here, researchers from the University of Colorado use their vast experience with optical lattice clocks to demonstrate a new strategy. They implement spin–orbit coupling in a 87Sr optical lattice clock using a narrow optical clock transition between two electronic states, avoiding the heating problems that plague other approaches. Although they use only a one-dimensional system, scaling the scheme up to larger systems could provide opportunities to simulate exotic condensed-matter phenomena. Engineered spin–orbit coupling (SOC) in cold-atom systems can enable the study of new synthetic materials and complex condensed matter phenomena1,2,3,4,5,6,7,8. However, spontaneous emission in alkali-atom spin–orbit-coupled systems is hindered by heating, limiting the observation of many-body effects1,2,5 and motivating research into potential alternatives9,10,11. Here we demonstrate that spin–orbit-coupled fermions can be engineered to occur naturally in a one-dimensional optical lattice clock12. In contrast to previous SOC experiments1,2,3,4,5,6,7,8,9,10,11, here the SOC is both generated and probed using a direct ultra-narrow optical clock transition between two electronic orbital states in 87Sr atoms. We use clock spectroscopy to prepare lattice band populations, internal electronic states and quasi-momenta, and to produce spin–orbit-coupled dynamics. The exceptionally long lifetime of the excited clock state (160 seconds) eliminates decoherence and atom loss from spontaneous emission at all relevant experimental timescales, allowing subsequent momentum- and spin-resolved in situ probing of the SOC band structure and eigenstates. We use these capabilities to study Bloch oscillations, spin–momentum locking and Van Hove singularities in the transition density of states. Our results lay the groundwork for using fermionic optical lattice clocks to probe new phases of matter.

Cite this article

Kolkowitz, S., Bromley, S., Bothwell, T. et al. Spin–orbit-coupled fermions in an optical lattice clock. Nature 542, 66–70 (2017). https://doi.org/10.1038/nature20811

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